1. Field of the Invention
The present invention is related to a Group III-V compound semiconductor, a method of manufacturing the same, and a light emitting element.
2. Description of the Background Art
Group III-V compound semiconductors, which are expressed by the following general formula InxGayAlzN (x+y+z=1, 0xe2x89xa6x less than 1, 0 less than yxe2x89xa61, 0xe2x89xa6z less than 1), are known as a material for a light emitting element such as a light emitting diode which emits ultraviolet light or blue light and a laser diode which emits ultraviolet light or blue light. Hereafter, x, y and z in the above mentioned general formula will be stated as In concentration, Ga concentration and Al concentration, respectively. Those in which the In concentration is 10% or more, in particular, are important for the purpose of display, since an emission wavelength in a visible range can be adjusted in accordance with the concentration of In.
However, big problems as described below have been impeding efforts to develop light emitting elements which use Group III-V compound semiconductors into a practical use. That is, first, no appropriate substrate has been found which can be used for growing crystal of a Group III-V compound semiconductor, and second, thermal stability of a Group III-V compound semiconductor is not excellent. Now, a detailed description will be given on these points.
Describing the first problem, despite the efforts to grow a Group III-V compound semiconductor on various substrates such as a sapphire substrate, a GaAs substrate and a ZnO substrate, since these substrates have largely different lattice constants and chemical characteristics from the Group III-V compound semiconductor, crystal of a sufficiently high quality has not been produced yet. To deal with this, an approach has been proposed which requires to grow GaN crystal which has a similar lattice constant and chemical characteristics to a Group III-V compound semiconductor first, and thereafter to grow a Group III-V compound semiconductor on the GaN crystal, so as to obtain excellent crystal (Japanese Examined Patent Publication No. 55-3834). However, it is known that a difference in lattice constant between the Group III-V compound semiconductor and GaN becomes larger an the In concentration increases, so that the crystal perfection deteriorates and the number of defects increases, even in this approach. Thus, it is difficult to manufacture a Group III-V compound semiconductor which has a high quality and a high In concentration.
Secondly, it is known that such compound semiconductors which contain In have substantially low decomposition temperatures than such compound semiconductors which do not contain In. For example, while GaN, AlN and mixed crystal of the two are relatively stable at a temperature of 1,000xc2x0 C. or higher, the thermal decomposition temperature of InN is about 600xc2x0 C. Although it depends on the In concentration, the compound semiconductors which contain In cause crystal deterioration at a temperature exceeding 1,000xc2x0 C. and create an increased number of defects, in general.
On the other hand, it is necessary to dispose a p-type current injection layer and an n-type current injection layer on both sides of an active layer to manufacture a light emitting element which is driven at a low voltage. As known in the art, while a compound semiconductor of n-type is easily manufactured, a compound semiconductor of p-type in very difficult to manufacture.
Further, to realize a high p-type conductivity, it is sometimes effective to perform post processing, such as thermal annealing or electron beam irradiation, on a layer which is doped with acceptor type impurities. In general, such processing is likely to be very effective when the layer which is doped with acceptor type impurities is exposed to a surface. Hence, it is preferable to grow the p-type current injection layer after forming the active layer. In addition, it is known that compound semiconductors which do not contain In more easily exhibit p-type conductivity than compound semiconductors which contain In.
For this reason, Gaxxe2x80x3Alyxe2x80x3N (xxe2x80x3+yxe2x80x3=1, 0 less than xxe2x80x3xe2x89xa61, 0xe2x89xa6yxe2x80x3 less than 1) which does not contain In is used an the p-type current injection layer. However, to obtain Gaxxe2x80x3Alyxe2x80x3N which exhibits excellent p-type conductivity, it is necessary to grow Gaxxe2x80x3Alyxe2x80x3N at a temperature exceeding 1,000xc2x0 C. Hence, while Gaxxe2x80x3Alyxe2x80x3N of p-type is grown at a temperature exceeding 1,000xc2x0 C., the active layer which contains In is deteriorated.
An object of the present invention is to obtain a Group III-V compound semiconductor which has a high quality and less defects, to obtain a method of manufacturing the same in which after an In containing layer is grown, CaAlN doped with p-type impurities is grown at a temperature exceeding 1000xc2x0 C., without deteriorating the In containing layer, so that a resultant Group III-V compound semiconductor exhibits an excellent emission characteristic, and further, to obtain a light emitting elements using such a Group III-V compound semiconductor which exhibits an excellent emission characteristic.
As a result of a wide range of study on Group III-V compound semiconductors, the inventors of the present invention have found that Group III-V compound semiconductor crystal which has a high quality and less defects is obtained if a Group III-V compound semiconductor has a specific laminated structure and if a Group III-V compound semiconductor which is expressed by a general formula InxGayAlzN (x+y+z=1, 0 less than x less than 1, 0 less than y less than 1, 0xe2x89xa6z less than 1), is a specific thin layer, and that the thermal stability of the compound semiconductors is improved if a GaAlN layer is grown at a relatively low temperature as a protection layer after a layer which contains In is grown.
That is, the present invention is directed to [1] a Group III-V compound semiconductor having a structure in which a first-layer, which is formed by a Group III-V compound semiconductor which is expressed by a general formula InxGayAlzN (x+y+z=1, 0 less than x less than 1, 0 less than y less than 1, 0xe2x89xa6z less than 1), a second-layer, which is formed by a Group III-V compound semiconductor which is expressed by a general formula Gaxxe2x80x2Alyxe2x80x2N (xxe2x80x2+yxe2x80x2=1, 0 less than xxe2x80x2xe2x89xa61, 0xe2x89xa6yxe2x80x2 less than 1), and a third-layer, which is formed by a Group III-V compound semiconductor which is expressed by a general formula Gaxxe2x80x3Alyxe2x80x3N (xxe2x80x3+yxe2x80x3=1, 0 less than xxe2x80x3xe2x89xa61, 0xe2x89xa6yxe2x80x3 less than 1), are stacked one atop the other in this order, and in which the first-layer has a thickness in the range between 5 xc3x85 and 90 xc3x85.
The present invention is also directed to [2] a Group III-V cond semiconductor having a structure in which a fifth-layer, which in formed by a Group III-V compound semiconductor which is expressed by a general formula GaaAlbN (a+b=1, 0xe2x89xa6axe2x89xa61, 0bxe2x89xa61), and a first-layer, which is formed by a Group III-V compound semiconductor which is expressed by a general formula InxGayAlzN (x+y+z=1, 0 less than x less than 1, 0 less than y less than 1, 0xe2x89xa6z less than 1), are stacked one atop the other in this order, and in which the first-layer has a thickness in the range between 5 xc3x85 and 90 xc3x85.
The present invention is also directed to [3] a Group III-V compound semiconductor having a structure in which a fifth-layer, which is formed by a Group III-V compound semiconductor which is expressed by a general formula GaaAlbN (a+b=1, 0xe2x89xa6axe2x89xa61, 0xe2x89xa6bxe2x89xa61), a fourth-layer having a lower impurity concentration than the fifth-layer, which is formed by a Group III-V compound semiconductor which is expressed by a general formula Gaaxe2x80x2Albxe2x80x2N (axe2x80x2+bxe2x80x2=1, 0xe2x89xa6axe2x80x2xe2x89xa61, 0xe2x89xa6bxe2x80x2xe2x89xa61), and a first-layer, which is formed by a Group III-V compound semiconductor which is expressed by a general formula InxGayAlzN (x+y+z=1, 0 less than x less than 1, 0 less than y less than 1, 0xe2x89xa6z less than 1), are stacked one atop the other in this order, and in which the first-layer has a thickness in the range between 5 xc3x85 and 90 xc3x85.
The present invention is also directed to [4] a Group III-V compound semiconductor having a structure in which a fifth-layer, which is formed by a Group III-V compound semiconductor which is expressed by a general formula GaaAlbN (a+b=1, 0xe2x89xa6axe2x89xa61, 0xe2x89xa6bxe2x89xa61), a fourth-layer having a lower impurity concentration than the fifth-layer, which is formed by a Group III-V compound semiconductor which is expressed by a general formula Gaaxe2x80x2Albxe2x80x2N (axe2x80x2+bxe2x80x2=1, 0xe2x89xa6axe2x80x2xe2x89xa61, 0xe2x89xa6bxe2x80x2xe2x89xa61), and a first-layer, which is formed by a Group III-V compound semiconductor which is expressed by a general formula InxGAyAlzN (x+y+z=1, 0 less than x less than 1, 0 less than y less than 1, 0xe2x89xa6z less than 1), a second-layer, which is formed by a Group III-V compound semiconductor which is expressed by a general formula Gaxxe2x80x2Alyxe2x80x2N (xxe2x80x2+yxe2x80x2=1, 0 less than xxe2x80x2xe2x89xa61, 0xe2x89xa6yxe2x80x2 less than 1), and a third-layer, which is formed by a Group III-V compound semiconductor which is expressed by a general formula Gaxxe2x80x3Alyxe2x80x3N (xxe2x80x3+yxe2x80x3=1, 0 less than xxe2x80x3xe2x89xa61, 0xe2x89xa6yxe2x80x3 less than 1), are stacked one atop the other in this order, and in which the first-layer has a thickness in the range between 5 xc3x85 and 90 xc3x85.
The present invention is also directed to [5] a method of manufacturing a Group III-V compound semiconductor in which after growing a first-layer which is formed by a Group III-V compound semiconductor which in expressed by a general formula InxGayAlzN (x+y+z=1, 0 less than x less than 1, 0 less than y less than 1, 0xe2x89xa6z less than 1), a third-layer which in formed by a Group III-V compound semiconductor which is expressed by a general formula Gaxxe2x80x3Alyxe2x80x3N (xxe2x80x3+yxe2x80x3=1, 0 less than xxe2x80x3xe2x89xa61, 0xe2x89xa6yxe2x80x3 less than 1) is grown at a temperature exceeding 1,000xc2x0 C., the method being characterized in that a second-layer which is formed by a Group III-V compound semiconductor which is expressed by a general formula GAxxe2x80x2Alyxe2x80x2N (xxe2x80x2+yxe2x80x2=1, 0 less than xxe2x80x2xe2x89xa61, 0xe2x89xa6yxe2x80x2 less than 1) is grown at 1,000xc2x0 C. or a lower temperature after growing the first-layer but before growing the third-layer.
Further, the present invention is directed to [6] a Group III-V compound semiconductor described in [1], [4] and [5] in which Mg concentration in a second-layer which is formed by a Group III-V compound semiconductor expressed by a general formula Gaxxe2x80x2Alyxe2x80x2N (xxe2x80x2+yxe2x80x2=1, 0 less than xxe2x80x2xe2x89xa61, 0xe2x89xa6yxe2x80x2 less than 1), is 1019/cm3 or less.
Still further, the present invention is directed to [7] a light emitting element which uses such a Group III-V compound semiconductor.
The Group III-V compound semiconductors according to the present invention have a high quality and less defects. Using these Group III-V compound semiconductors, it is possible to provide for a light emitting element which has a high luminescence efficiency and an excellent emission characteristic.
In addition, according to the methods of manufacturing a Group III-V compound semiconductor according to the present invention, even if GaAlN doped with p-type impurities is grown at a temperature exceeding 1,000xc2x0 C. after growing a layer which contains In, the In containing layer does not deteriorate, so that a Group III-V compound semiconductor which has a high quality and less defects is obtained.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.